1. Field of the Invention
This invention relates to an improvement of fixing apparatus for a copying machine and, more particularly, to an improvement of a bearing device of a fixing roll or a heated roll including a heater therewithin.
2. Description of Prior Art
A fixing apparatus having a rotatable hollow fixing roll including therewithin a heating means having such a heating source as an infrared generating device, nickel-chromium heating wire, or a halogen lamp for heating the surface of the fixing roll from the inside is well known in the art of fixing powder images carried on a copying paper. Fixing is effected by driving the fixing roll and an associated back-up roll in pressure contact with the fixing roll with a copying sheet fed therebetween. Since the heat conduction to the bearing directly through the fixing roll causes the grease contained as lubricant in the bearing to be deteriorated, resulting in the damage of the bearing, an adiabatic resin member is also provided in the born part of the fixing roll for preventing the heat retained in the fixing roll from conducting to the bearing or other mechanical members through the bearing. But, in such device it has been found that the life of the adiabatic member is relatively limited. In electrophotographic copying machines which is able to reproduce a number of copies sequentially, the surface temperature of the fixing roll, generally, rises to 150.degree. C to 200.degree. C and as the result the adiabatic resin member is heated directly through the born part of the fixing roll heated by the heating means, causing the adiabatic member to expand not only in the radial direction but in the axial direction. Also, the fixing roll itself expands due to the heat so as to apply compression forces to the adiabatic member. Furthermore, the adiabatic member is subject to compression forces resulting from the fixing roll pressing the copying sheet against each other during the fixing process. The combination of these forces produces a great magnitude of compression force having a tendency to deform the adiabatic member within a relatively short period, causing the bearing part to loose and render its usage impossible and to apply a great magnitude of stress concentratedly to the portions of the adiabatic member at which the adiabatic member is in contact with the edges of the inner ring, causing the adiabatic member to be torn off or destroyed. Moreover, the inner ring of the bearing provided as a rotary bearing is disposed in pressure contact with the adiabatic member. This also increases the deformation of the adiabatic member.